KR20220030285A - Manufacturing method of molten iron by electric furnace - Google Patents

Abstract

In an electric furnace, molten iron is produced at low cost with high energy utilization efficiency.
In an electric furnace in which a shaft-type preheating chamber 2 is extended above the melting chamber 1 to preheat the iron-based scrap (x), the exhaust gas generated in the melting chamber (1) is preheated in which the iron-based scrap (x) is charged. The iron-based scrap (x) is preheated by passing it through the chamber (2), and the preheated iron-based scrap (x) is sequentially descended in the preheating chamber (2) to be supplied into the melting chamber (1), and in the melting chamber (1) As a method of obtaining molten iron (m) by melting, the apparent bulk density of iron-based scrap (x) filled in the preheating chamber (2) is 0.50 t/m3 or more and less than 1.00t/m3, and in the preheating chamber (2) The iron-based scrap (x) is charged in the preheating chamber (2) so that the iron-based scrap filling ratio H _SC /H _SF of A carbon material is used as an auxiliary|assistant heat source, and oxygen and a carbon material are blown into the melting chamber 1 so that carbon/oxygen ratio C/O may become 0.70 or more.

Description

Manufacturing method of molten iron by electric furnace

The present invention relates to a method for producing molten iron by melting iron-based scrap in an electric furnace.

In an electric furnace, molten iron is produced by melting iron-based scrap (cold iron source) with arc heat, but a large amount of electric power is consumed to generate arc heat. Conventionally, in order to suppress power consumption in an electric furnace, a method of preheating iron-based scrap with high-temperature flue gas generated during melting, and a method of blowing (blowing) carbon materials such as coke as an auxiliary heat source and the like are employed.

As a method of melting iron-based scrap while preheating the iron-based scrap with high-temperature exhaust gas generated during melting, the following method is known. In this method, the iron-based scrap preheating chamber is blown over the upper part of the melting chamber, and the high-temperature exhaust gas generated in the melting chamber is passed through the preheating chamber filled with the iron-based scrap to preheat the iron-based scrap, and the preheated This is to ensure that iron-based scrap is supplied to the melting chamber.

Regarding this method of dissolving iron-based scrap, Patent Document 1 discloses a method of adjusting the type or blending amount of iron-based scrap so that the filling state of the iron-based scrap in the preheating chamber becomes 0.7 t/m3 or more in terms of the apparent bulk density. has been disclosed. According to this method of melting iron-based scrap, it is said that energy utilization efficiency is high and it is effective also in reduction of manufacturing cost. Moreover, in the method of this patent document 1, blowing in a carbon|charcoal material into a melting chamber, and using it as an auxiliary|assistant heat source is also performed.

Patent Document 1: Japanese Patent Laid-Open No. 2012-180560

In recent years, in the operation of electric furnaces, improvement in energy efficiency and reduction in power consumption are strongly demanded also in terms of global environmental problems. . However, as a result of investigation by the inventors, it has been found that, as in Patent Document 1, merely regulating the packing density (apparent bulk density) of iron-based scrap in the preheating chamber is insufficient in terms of energy utilization efficiency, and further increase in efficiency is required. . That is, to obtain high energy use efficiency, not only the packing density (apparent bulk density) of the iron-based scrap in the preheating chamber, but also the charging height of the iron-based scrap in the preheating chamber, and the supply of carbon material (auxiliary heat source) and oxygen into the melting chamber It turned out that conditions were also important factors. Therefore, it is necessary to optimize the operating conditions including these.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above, and in a method for manufacturing molten iron by an electric furnace having a preheating chamber for preheating iron-based scrap with furnace flue gas, molten iron with high energy use efficiency It is to provide a manufacturing method of molten iron which can manufacture molten iron and can also reduce the manufacturing cost of molten iron.

As a result of repeated intensive studies to solve the above problems, the inventors found that, in addition to the packing density (apparent bulk density) of the iron-based scrap in the preheating chamber, the iron-based scrap filling ratio (filling height) in the preheating chamber, and the melting chamber It has been discovered that high energy utilization efficiency can be obtained by optimizing the supply ratio of the carbon material (auxiliary heat source) and oxygen into the furnace.

This invention has been made based on such knowledge, and makes the following into a summary.

[1] A melting chamber (1) for melting iron-based scrap by arc heating, and a shaft-type preheating chamber (2) extended above the melting chamber (1) to preheat iron-based scrap In an electric furnace equipped with The iron-based scrap is preheated by passing gas through the preheating chamber 2 filled with iron-based scrap, and the preheated iron-based scrap is sequentially descended in the preheating chamber 2 to enter the melting chamber 1 As a method of obtaining molten iron by supplying and dissolving iron-based scrap in a melting chamber (1),

The apparent bulk density P of the iron-based scrap filled in the preheating chamber 2 is 0.50t/m3 or more and less than 1.00t/m3, and the iron-based scrap filling ratio H in the preheating chamber 2 _SC /H _SF (however, H _SC : filling height of iron scrap in preheating chamber [m], H _SF : height in preheating chamber [m]) is 0.5 to 0.8, iron scrap in preheating chamber 2 is charged,

Carbon material is used as an auxiliary heat source for dissolving iron-based scrap in the melting chamber 1, and in the melting chamber 1, the carbon/oxygen ratio C/O (however, C: the amount of carbon in the carbon material [kg], O: A method for producing molten iron by an electric furnace, comprising blowing (blowing) oxygen and carbon ash so that the oxygen blowing amount [Nm 3 ]) is 0.70 or more.

[2] The method for producing molten iron by an electric furnace according to the production method of [1] above, wherein the oxygen concentration in the preheating chamber (2) is less than 15 vol%.

[3] In the manufacturing method of [1] or [2] above, the amount of carbon material blown into the melting chamber 1 is 0.3 to 1.4 (kg/min)/ton of hot water, and the amount of oxygen blown is 20 to 40 ( A method for producing molten iron by an electric furnace, characterized in that it is Nm3/hr)/ton of tapping.

[4] In the manufacturing method of any one of [1] to [3] above, at least one supporting smoke burner is installed in the melting chamber 1, and the iron-based scrap and molten iron in the melting chamber are removed by the supporting burner. A method for producing molten iron by an electric furnace, comprising heating.

[5] In the manufacturing method according to any one of [1] to [4] above, in the electric furnace, the preheating chamber 2 extends above the position away from the arc heating part of the melting chamber 1, and the preheating chamber ( 2) a scrap charging port 20 is installed in the upper part,

The iron-based scrap charged into the preheating chamber 2 from the scrap charging port 20 is filled in the preheating chamber 2 and the space portion 1a of the melting chamber 1 below the preheating chamber 2, A method of manufacturing molten iron by an electric furnace, characterized in that the iron-based scrap of the space portion (1a) is sequentially extruded toward the arc heating unit.

[6] The method for manufacturing molten iron by an electric furnace according to the manufacturing method of [5] above, wherein the iron-based scrap of the space portion 1a is sequentially extruded toward the arc heating unit by the extruder (3).

According to the present invention, in the method for manufacturing molten iron by an electric furnace having a preheating chamber for preheating iron-based scrap with furnace flue gas, molten iron can be manufactured with high energy use efficiency and the manufacturing cost of molten iron can be reduced there is.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows typically the electric furnace which concerns on one Embodiment of this invention in the state which carried out the longitudinal section.

The method for manufacturing molten iron based on the present invention includes a melting chamber 1 for melting iron-based scrap by arc heating, and a shaft-type preheating chamber extending above the melting chamber 1 for preheating iron-based scrap ( In the electric furnace having 2), iron-based scrap is sequentially charged into the preheating chamber 2, so that the iron-based scrap is charged in the preheating chamber 2, and the exhaust gas generated in the melting chamber 1 is filled with the iron-based scrap. The iron-based scrap is preheated by passing it through the preheating chamber (2), and the preheated iron-based scrap is sequentially descended in the preheating chamber (2) to be supplied into the melting chamber (1), and the iron-based scrap is melted in the melting chamber (1). to obtain molten iron. In addition, in this manufacturing method, the carbon material (auxiliary heat source) and oxygen are blown into the melting chamber 1 . In the present invention, in this molten iron manufacturing process, the apparent bulk density (P) of the iron-based scrap filled in the preheating chamber 2 and the iron-based scrap filling ratio H _SC /H _SF (however, H _SC : iron-based scrap in the preheating chamber 2 ) of filling height [m], H _SF : height in preheating chamber [m]), and carbon/oxygen ratio C/O for carbon material and oxygen blown into melting chamber 1 (however, C: carbon content in carbon material [ kg], O: to optimize the amount of oxygen blowing [Nm3]).

In the present invention, the apparent bulk density (P) of the iron-based scrap filled in the preheating chamber (2) is 0.50t/m3 or more and less than 1.00t/m3, and the iron-based scrap filling ratio in the preheating chamber (2) is H _SC The iron-based scrap is charged into the preheating chamber 2 so that /H _SF (however, H _SC : the filling height of the iron-based scrap in the preheating chamber, H _SF : the height in the preheating chamber) is 0.5 to 0.8.

There are various shapes and sizes of iron scraps (for example, those stipulated in the "Standards for Inspection of Iron Scraps" of the Japan Iron Works Association), and they are appropriately combined and mixed. and charging in the preheating chamber 2 so that the apparent bulk density P of the iron-based scrap filled layer in the preheating chamber 2 is 0.50 t/m 3 or more and less than 1.00 t/m 3 .

The apparent bulk density (P) of iron-based scrap is (P) = Σ (mass i) / Σ (volume i) = Σ (mass i) / Σ (mass i / bulk density i). Here, the unit of mass is [t], the unit of volume is [m3], the unit of bulk density is [t/m3], and i indicates the type of scrap to be charged. For example, among the heavy, press, shredder, new cutting, steel processing chips, and old wire stipulated in the "Standards for Inspection of Iron Scraps" of the Japan Iron Works Association to be charged. In the case of two or more types, their bulk density is obtained in advance, and the apparent bulk density (P) of the iron-based scrap can be obtained from the bulk density and the mixing ratio [mass%] of each type of scrap in the charged iron-based scrap. That is, apparent bulk density (P) = (heavy bulk density) x (heavy blending ratio) + (pressing bulk density) x (pressing blending ratio) + (shredder bulk density) x (shredder blending ratio) + (new end bulk density) It is computable according to x (strength processing powder mixing ratio) + (strength processing powder bulk density) x (steel processing powder mixing ratio) + (high wire bulk density) x (high wire mixing ratio). The bulk density of each type of scrap is, for example, put into a large container of a fixed capacity, the target scrap is measured, the mass is measured, and what is necessary is just to calculate|require it from the volume and mass.

In addition, the iron-based scrap melted in the present invention includes, for example, iron such as direct reduced iron and cold iron as a main component, in addition to the scrap prescribed in the "Iron Scrap Inspection Uniform Standard" of the Japan Iron Works Association mentioned above. may be included. Similarly, the abnormal part of the cast steel cast by continuous casting or the ingot method, and the crop and molten iron produced by the rolling of steel materials such as steel strips Calcium debris generated at a steel mill, such as pig iron that has been hardened, may be contained. Scraps other than those stipulated in these "Standards for Inspection of Iron Scraps" are classified as other scrap types, if necessary, and their bulk density is calculated. Moreover, although the energy of the part which reduces iron oxide costs extra what contains a lot of iron oxide powder, what is necessary is just to consider operation cost etc., and just to use it suitably.

In addition, classification of the scrap type does not necessarily have to be based on the "iron scrap inspection unified standard", and may be classified according to an arbitrary standard according to the bulk density. In other words, in the classification of the specified scrap species, the bulk density is obtained for each scrap type, and the apparent bulk density (P) of the iron-based scrap filled in the preheating chamber 2 is calculated based on this bulk density and the mixing ratio of each scrap type. save it

Here, even when the apparent bulk density (P) is less than 0.50 t/m 3 or more than 1.00 t/m 3 , the heat transfer efficiency between the flue-gas and the iron-based scrap deteriorates, and the preheating chamber 2 heats up sufficiently with the iron-based scrap. The high-temperature exhaust gas that is not used is discharged, and the preheating efficiency is lowered. That is, when the apparent bulk density P is less than 0.50 t/m 3 , the heat transfer efficiency from the exhaust gas to the iron-based scrap filled in the preheating chamber 2 is low, and the exhaust gas leaks at a high temperature and passes through the preheating chamber 2 . As a result, the preheating efficiency decreases. On the other hand, when the apparent bulk density P becomes 1.00 t/m 3 or more, the preheating efficiency decreases due to pressure loss. In this way, even if the apparent bulk density P is too small or too large, the preheating efficiency will decrease. In this case, it is necessary to secure the preheating temperature by slowing down the falling speed of the iron-based scrap in the preheating chamber 2 , but in this way, the iron-based scrap is excessively oxidized in the preheating chamber 2 . And the energy loss for reducing this oxidized iron-type scrap will generate|occur|produce. In addition, if the iron-based scrap in the preheating chamber 2 is oxidized excessively, some iron-based scrap is melted due to oxidative heat generation, and the descent of the iron-based scrap in the preheating chamber 2 is stopped by fusion to the surrounding iron-based scrap. There is a risk of causing trouble to throw away. When such a jamming occurs, since the iron-based scrap does not descend until the jamming is eliminated, the iron-based scrap in the preheating chamber 2 continues to be preheated, further promoting iron oxidation, and further jamming. Moreover, since electric power is continuously supplied even while it is engaged, useless energy is consumed. In addition, from the above viewpoints, the particularly preferable apparent bulk density P is in the range of 0.60 to 0.80 t/m 3 .

In addition, iron-based scrap is charged into the preheating chamber 2 so that the iron-based scrap filling ratio H _SC /H _SF in the preheating chamber 2 is always kept in the range of 0.5 to 0.8, preferably in the range of 0.6 to 0.8. When the iron-based scrap filling ratio H _SC /H _SF in the preheating chamber 2 is less than 0.5, the heat transfer efficiency from the exhaust gas to the iron-based scrap filled in the preheating chamber 2 is low, and the exhaust gas leaks at a high temperature to preheat Since it passes through the seal 2, the preheating efficiency decreases. Therefore, also in this case, it is necessary to secure the preheating temperature by slowing down the falling speed of the iron-based scrap in the preheating chamber 2 . As a result, as described above, excessive oxidation of iron-based scrap occurs in the preheating chamber 2, and energy loss for reducing the oxidized iron-based scrap occurs. In addition, if the iron-based scrap in the preheating chamber 2 is excessively oxidized, there is a risk of jamming as described above. On the other hand, if the iron-based scrap filling ratio H _SC /H _SF exceeds 0.8, there is a risk of problems such as not properly closing the preheating chamber gate (the scrap charging port 20 of the embodiment to be described later) after the iron-based scrap is charged. . If the preheating chamber gate is not properly closed, the exhaust gas or dust originally exhausted from the preheating chamber 2 through the duct is dissipated from the preheating chamber gate.

During operation, the iron-based scrap preheated in the preheating chamber 2 is sequentially descended and supplied to the melting chamber 1 . Accordingly, since the filling height of the iron-based scrap in the preheating chamber 2 is reduced, new iron-based scrap is charged into the preheating chamber 2 at a predetermined timing. Then, new iron-based scrap is charged so that the iron-based scrap filling ratio H _SC /H _SF in the preheating chamber 2 is always maintained in the range of 0.5 to 0.8. For this purpose, as will be described later, it is preferable to utilize a monitoring camera or the like that monitors the level of the top surface of the iron-based scrap filled layer in the preheating chamber 2 .

Further, in the present invention, carbon material is used as an auxiliary heat source for melting iron-based scrap in the melting chamber 1, and in the melting chamber 1, the carbon/oxygen ratio C/O (however, C: carbon amount in the carbon material) [kg], O: Oxygen (pure oxygen) and carbon material are blown so that the amount of oxygen injected [Nm3]) is 0.70 or more. In addition, when using not pure oxygen but oxygen-containing gas (for example, the mixed gas of pure oxygen and air), the oxygen injection amount O is the injection amount of the oxygen part in oxygen-containing gas.

Usually, the carbon material and oxygen are blown using a blowing lance, respectively, but as will be described later, a method of injecting from above the melting chamber 1, a method of injecting from a bottom injection nozzle, etc. Blowing may be performed with

Here, when the carbon/oxygen ratio C/O is too small, the oxygen concentration in the exhaust gas increases due to unreacted oxygen. For this reason, the oxygen concentration in the preheating chamber 2 through which the exhaust gas flows increases, and the oxidizing atmosphere in the preheating chamber 2 becomes an oxidizing atmosphere, resulting in excessive oxidation of iron-based scrap, resulting in loss of energy for reducing the oxidized iron-based scrap. throw it away In addition, as described above, when the iron-based scrap in the preheating chamber 2 is excessively oxidized, some iron-based scrap is melted due to oxidative heat generation and fused to the surrounding iron-based scrap, thereby reducing the drop of the iron-based scrap in the preheating chamber 2 . There is a possibility that a trouble (jamming) that stops may occur. When the carbon/oxygen ratio C/O is less than 0.70, the above problem tends to occur. In addition, from the above viewpoint, the carbon/oxygen ratio C/O is particularly preferably in the range of 0.75 to 0.80. In addition, although the upper limit of carbon/oxygen ratio C/O is not specifically limited, It is preferable to operate at less than 2.0.

As described above, when the oxygen concentration in the preheating chamber 2 is high, the iron-based scrap is oxidized excessively, resulting in energy loss for reducing the oxidized iron-based scrap. For this reason, it is preferable that the oxygen concentration in the preheating chamber 2 is less than 15 vol%.

In addition, in blowing the carbon material and oxygen into the melting chamber 1 as described above, if the amount of carbon material injected is too small, the function as an auxiliary heat source cannot be sufficiently exhibited. is cooled, and the reduction reaction becomes excessive and the efficiency of operation decreases. Moreover, when there are too few oxygen injection amounts, the scrap dissolution efficiency by oxidation reaction heat will fall, and operation efficiency will fall. On the other hand, when there is too much oxygen blowing amount, splashing of molten slag and molten iron will generate|occur|produce excessively, and there exists a possibility that equipment troubles, such as damage to a furnace body and damage to a cooling installation, may be caused. For this reason, it is preferable that the amount of blowing of the carbon material is about 0.3 to 1.4 (kg/min)/ton of tapping, and the amount of blowing of oxygen is about 20 to 40 (Nm3/hr)/ton of tapping.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows typically one Embodiment of this invention in the state which cross-sectioned the electric furnace longitudinally.

The electric furnace includes a melting chamber 1 for melting iron-based scrap by arc heating, and a preheating chamber 2 for preheating iron-based scrap supplied to the melting chamber 1 .

The upper part of the melting chamber 1 is covered with the furnace cover 4 of the water-cooled structure which can open and close. In the substantially central portion of the melting chamber 1, a plurality of electrodes 5 are inserted through the furnace cover 4 from above, and an arc is blown between the electrodes 5 to melt iron-based scrap. An arc heating unit (A) is configured. Usually, the electrode 5 is made of graphite or the like, and is movable up and down.

A shaft-type preheating chamber 2 is extended in the upper part of the melting chamber 1 at a position away from the arc heating unit A, and this preheating chamber 2 has a vertical relationship with the melting chamber 1 . is connected with An openable and openable scrap charging port 20 is installed at an upper portion of the preheating chamber 2 . In addition, an exhaust port 21 is provided on the upper side of the preheating chamber 2 , and an exhaust duct 6 is connected to the exhaust port 21 . This exhaust duct 6 is connected to a suction blower (not shown), and the high-temperature exhaust gas generated in the melting chamber 1 by suction by the suction blower flows into the preheating chamber 2, After passing through the preheating chamber 2 , it is exhausted from the exhaust duct 6 . In addition, a dust collector (not shown) is provided in the middle of the exhaust duct 6 .

Above the preheating chamber 2, an open-bottom supply bucket 13 suspended from the traveling cart 16 can move, and from this supply bucket 13, the scrap charging port 20 The iron-based scrap (x) is charged in the preheating chamber (2) through the.

In the melting chamber 1, facing the space portion 1a of the lower side of the preheating chamber 2, the iron-based scrap x filled in the space portion 1a is fed by the electrode 5. The extruder 3 (pusher) for extruding to the arc heating part A side is provided. This extruder 3 penetrates the side wall of the melting chamber 1, is installed so as to advance and retreat in the direction of the arc heating unit A (in this embodiment, in the furnace center direction), and is driven by a driving device (not shown). and extruding the iron-based scrap (x) in the space portion (1a) from the tip to the arc heating unit (A) side.

In addition, for example, without installing the extruder 3, the inside of the space portion 1a is generated by the weight of the iron-based scrap x filled in the preheating chamber 2 and the space portion 1a. The iron-based scrap (x) may be naturally extruded toward the arc heating unit (A).

In the melting chamber 1, an oxygen blowing lance 7 and a carbon material blowing lance 8 are inserted through the furnace lid 4 from above.

From the carbon material blowing lance 8, the carbon material which consists of 1 or more types, such as coke, char, coal, charcoal, graphite, using air, nitrogen, etc. as a conveyance gas, is molten slag (s) is taken in Moreover, oxygen is supplied (jetted) from the oxygen blowing lance 7, molten slag is pushed by this oxygen, and oxygen is blown into the molten iron m.

In addition, as described above, from the oxygen blowing lance 7, you may blow in oxygen-containing gas (for example, mixed gas of pure oxygen and air) instead of pure oxygen.

In the melting chamber 1, a hot water outlet 11 is provided at the furnace bottom on the opposite side to the side on which the preheating chamber 2 is installed, and an outlet 11 is provided at an upper side wall thereof. ) (12) are provided, respectively. These hot water outlets 11 and 12 are closed by the filling sand or mud material filled inside, and the hot water door 14 and the outlet door 15 which block this from the outside. .

At a position almost immediately above the hot water outlet 11 , a supporting smoke burner 9 inserted into the melting chamber 1 through the furnace cover 4 from above is provided. This supporting smoke burner 9 melts fossil fuels, such as heavy oil, kerosene, pulverized coal, propane gas, and natural gas, with delayed gas (oxygen, air, or oxygen-enriched air). It is to be burned in the chamber (1). For example, when the molten iron m is tapped, undissolved iron-based scrap may remain, and in such a case, the supporting burner 9 can help dissolve the iron-based scrap.

The inner wall of the electric furnace 1 is composed of a refractory material, and the furnace wall 10 of the melting chamber 1 has a water cooling structure.

At least one supporting burner 9 is installed in the melting chamber 1 and is used to heat the iron-based scrap (x) and molten iron (m) in the melting chamber (1). In a general electric furnace in which the preheating chamber (2) is not attached, it is common to install the supporting smoke burner (9). The ignition efficiency of the combustion heat of the supporting smoke burner 9 is about 20-50%, and among the combustion heat of the supporting smoke burner 9, most of the unburned heat is dissipated as flue gas sensible heat. become (放散) On the other hand, in the electric furnace having the preheating chamber 2 as in the present invention, there is an advantage in that the high temperature flue gas sensible heat can be melted while igniting the iron-based scrap (x). Therefore, among the combustion heat of the supporting smoke burner 9, the unburned component can also contribute to the preheating of the iron-based scrap x. This can be achieved by properly maintaining the apparent bulk density P of the iron-based scrap x filled in the preheating chamber 2 . At this time, the heating efficiency of the supporting smoke burner 9 may be improved by 50 to 80% in total.

Operation is possible even without the supporting burner 9 . However, if the supporting burner 9 is not used, the iron-based scrap around the electrode 5 is quickly dissolved, but there are cases where the iron-based scrap melts and remains in a place away from the electrode 5, that is, in a cold spot. Therefore, when a non-uniformity generate|occur|produces in the scrap melting|dissolution rate in a furnace, an operation time may be extended and an electric power source unit may deteriorate. That is, the supporting smoke burner 9 can be provided at the position of the cold spot, and the cold spot can be eliminated using the supporting smoke burner 9 . Therefore, it is preferable to install and use the supporting smoke burner 9 . In addition, as in the present invention, if the carbon/oxygen ratio C/O is controlled and the oxygen concentration in the preheating chamber 2 is less than 15%, the higher the flue gas temperature in the preheating chamber 2, the iron-based scrap can be sufficiently preheated. . As described above, among the combustion heat of the supporting smoke burner 9 , an unburned component may also contribute to the preheating of the iron-based scrap x. However, if the supporting smoke burner 9 is not used, the iron-based scrap x in the preheating chamber 2 is not sufficiently preheated and is charged into the melting chamber 1 depending on the operating conditions. There is a possibility that non-uniformity may occur in speed.

In the operation (manufacture of molten iron) of the electric furnace of this embodiment, the arc heating part A is comprised by the some electrode 5 in the melting chamber 1, This is made into a main heat source, and a cold iron source is used. (x) dissolves. Further, the carbon material is blown into the molten slag s from the carbon material blowing lance 8, and is used as an auxiliary heat source. On the other hand, oxygen is blown into the molten iron m from the oxygen blowing lance 7, and the molten iron is decarburized to a predetermined amount of carbon by the oxygen. At this time, oxygen and carbon|charcoal material are blown in from each lance 7 and 8 so that carbon/oxygen ratio C/O may become 0.70 or more. In addition, in order to dissolve the undissolved iron-based scrap x, a smoke burner 9 is used as appropriate as necessary. By the dissolution treatment of the iron-based scrap x in the dissolution chamber 1 as described above, high-temperature exhaust gas including CO, CO ₂ , unreacted O ₂ or outside air flowing in from an opening or the like is generated. do.

The charging of the iron-based scrap x, which is a raw material of molten iron, into the electric furnace is performed using the supply bucket 13 . The iron-based scrap (x) is temporarily placed in a place where the scrap is placed, and among them, the iron-based scrap (x) of a predetermined type and mass ratio is blended according to the type of molten iron to be manufactured. In the present invention, the iron-based scrap (x) is blended so that the apparent bulk density (P) of the iron-based scrap filled in the preheating chamber 2 is 0.50 t/m3 or more and less than 1.00t/m3, and the supply bucket 13 ) is entered.

The supply bucket 13 in which the iron scrap (x) is put is moved directly above the preheating chamber 2 by the traveling bogie 16, and from this supply bucket 13, through the open scrap charging port 20 The iron-based scrap (x) is charged into the preheating chamber (2). As shown in FIG. 1 , the iron-based scrap x charged from the scrap charging port 20 is in a state of being filled in the space portion 1a of the preheating chamber 2 and the melting chamber 1 below it.

The charging state of the iron-based scrap x in the preheating chamber 2 is managed so that the iron-based scrap filling ratio H _SC /H _SF is 0.5 to 0.8. That is, during operation, the iron-based scrap x preheated in the preheating chamber 2 is sequentially descended and supplied to the melting chamber 1 , and accordingly, the filling height of the iron-based scrap in the preheating chamber 2 is reduced. . Therefore, new iron-based scrap x is charged into the preheating chamber 2 at a predetermined timing so that the iron-based scrap filling ratio H _SC /H _SF in the preheating chamber 2 is always maintained in the range of 0.5 to 0.8, The iron-based scrap (x) is charged. For this reason, a monitoring camera that monitors the top level of the filled layer of iron scrap in the preheating chamber 2 or a sensor capable of detecting the top level is installed, and based on the information, a predetermined amount of new iron scrap ( It is preferable to charge x) at a predetermined timing.

In addition, an organic substance (for example, plastic, rubber, biomass, etc.) may mix in the iron-type scrap x charged into the electric furnace (preheating chamber 2).

The high-temperature exhaust gas generated when the iron-based scrap x is melted in the melting chamber 1 flows into the preheating chamber 2 by suction of the exhaust gas as described above, rises in the preheating chamber 2, and then through the exhaust port (21) is exhausted. In the process, the iron-based scrap x charged in the preheating chamber 2 is preheated. In the case of this embodiment, the temperature of the exhaust gas flowing into the preheating chamber 2 is about 1000-1500 degreeC.

As the melting progress of the iron-based scrap x in the arc heating section A in the melting chamber 1, the iron-based scrap x filled in the space portion 1a of the melting chamber 1 is removed by the extruder 3 ) to sequentially extrude to the arc heating unit (A) side. Accordingly, the iron-based scrap (x) charged in the preheating chamber 2 is sequentially descended. Accordingly, as described above, new iron-based scrap (x) is charged into the preheating chamber 2 by the supply bucket 13 as described above. and do this repeatedly. When the melting of the iron-based scrap (x) proceeds and a predetermined amount (one charge) of molten iron is collected in the melting chamber (1), the iron-based scrap (x) is transferred to the space of the preheating chamber (2) and the melting chamber (1) ( While maintaining the state filled in 1a), the molten iron m is tapped from the tap 11 , and the molten slag s is poured from the tap 12 .

In addition, at the start of operation of the electric furnace, in order to uniformly charge the iron-based scrap into the melting chamber 1 , with the furnace cover 4 open, the melting chamber 2 opposite to the preheating chamber 2 Iron-based scrap or carbon material may be charged into the space, and molten iron may be charged into the melting chamber 1 at the time of charging this iron-based scrap. This molten iron can be charged into the melting chamber 1 by a ladle for supply (not shown) or a molten iron pipe (not shown) leading to the melting chamber 1 .

As a method of adding carbonaceous material or oxygen, in addition to the lance blowing method as in the present embodiment, a method of injecting into the bath from above the melting chamber 1, a dedicated nozzle is provided at the bottom of the furnace, You may employ the method of floor-spray injection, etc. In addition, although the blowing lance of carbon material and oxygen may be immersed in molten slag or molten iron, it is not immersed in molten slag or molten iron as in this embodiment, but follows according to the level change of the molten metal surface of molten slag or molten iron.從) can be done in this way. Moreover, the system which installs an oxygen blowing lance in a furnace wall and blows oxygen from a furnace wall may be sufficient.

As a type of electric furnace, there are a direct current type and an alternating current type, and since the electric furnace of this embodiment is an alternating current type, it has the electrode 5 as mentioned above. On the other hand, when the electric furnace is a direct current type, electrodes are present at each of the furnace bottom and upper part, and an arc is blown between the electrodes to melt the cold iron source. The present invention can also be applied to the production of molten iron by such a direct current electric furnace.

In addition, if the present invention is a method of preheating the iron-based scrap (x) by guiding the exhaust gas generated in the melting chamber (1) to the preheating chamber (2), there is no limitation on the type of electric furnace to be used, for example, the melting chamber It is applicable to the manufacturing method of molten iron using various types of electric furnaces, such as a manufacturing method of molten iron using an electric furnace which does not have this extruder.

Example

In the electric furnace facility provided with the melting chamber 1 and the preheating chamber 2 as shown in FIG. 1, the iron-type scrap (x) was melt|dissolved, and molten iron was manufactured. The equipment specifications of this electric furnace installation are shown below.

Melting chamber: furnace diameter 7m, furnace height 5m

Preheating room: 3m wide, 4m deep, 5m high

Furnace capacity: 210 tons

Power: AC 50Hz

Trans capacity: 75MVA

Number of electrodes: 3

In the melting chamber 1 and the preheating chamber 2, 210 tons of iron-based scrap were charged, and an arc was generated by the electrode 5 (upper graphite electrode) to melt the iron-based scrap. Further, pure oxygen is supplied from the oxygen blowing lance 7 at 3000 to 5000 Nm3/hr, and coke powder is supplied from the carbon material blowing lance 8 at 60 to 70 kg/min. took in During operation, the inside of the preheating chamber 2 is monitored with a monitoring camera, and when the iron-based scrap filled in the preheating chamber 2 is sequentially descended due to the dissolution of the iron-based scrap in the melting chamber 1, the supply bucket ( 13), the new iron-based scrap transferred to the preheating chamber was supplied into the preheating chamber 2 from the scrap charging port 20 above the preheating chamber, and the filling height of the iron-based scrap in the preheating chamber 2 was maintained within a certain range. .

As the coke powder blown from the carbon material blowing lance 8, a fixed carbon content of 85 mass% or more, a moisture content of 1.0 mass% or less, a volatile matter content of 1.5 mass% or less, and an average particle size of 5 mm or less were used. Moreover, in order to melt|dissolve the iron-type scrap (x) and heat the molten iron (m), the supporting combustion burner 9 was used suitably as needed. The number of installations of the supporting smoke burner 9 was one, and the amount of combustion was used at 2000 Mcal/hr per one supporting smoke burner.

In the stage where 210 tons of molten iron is generated in the melting chamber 1 by dissolving under the condition that iron-based scrap is continuously present in the melting chamber 1 (space portion 1a) and in the preheating chamber 2 , leaving 80 tons in the furnace, and tapping 130 tons of molten iron for one charge with a ladle from the tapping port 11. It operated so that the temperature of molten iron at the time of tapping was about 1600 degreeC, and the C concentration in molten iron might be 0.060 mass%.

Dissolution of iron-based scrap was continued, performing sending acid and coke blowing even after 130 tons of tapping, and when the amount of molten iron in the melting chamber 1 reached 210 tons again, tapping of 130 tons was repeated.

As the iron-based scrap, the bulk density was determined based on the scrap type stipulated in the "Unified Standards for Inspection of Iron Scraps" of the Japan Iron Works Association, and two or more types of the following scraps (i) to (iv) were blended.

(i) Heavy: It is sized by guillotine shearing machine, gas melting cutting machine, heavy machine cutting machine, etc., and it is divided into HS, H1-H4 according to thickness, size, and single weight, but in this embodiment , "HS: thickness 6 mm or more, width or height 500 mm or less x length 700 mm or less", "H4: thickness less than 1 mm, width or height 500 mm or less x length 1200 mm or less" is used in combination did The bulk density was 0.5 t/m 3 .

(ii) Shredder: This is iron scrap that is mainly made of steel plate processed products as a base material, shredded by a shredder machine, and then sorted by a magnetic separator. The bulk density was 1.3 t/m 3 .

(iii) New end: Cutting chips and punching chips generated when manufacturing a steel plate processed product. According to the shape and degree of oxidation, it is divided into press A, press B, bar A, bar B, etc., but in this embodiment, "Press A: The sum of the three sides is 1800 mm or less and the maximum side is 800 mm or less, and is not oxidized with a thin steel plate that has not been subjected to surface treatment", "Bar A: Width or height 500 mm or less × length It was 1200 mm or less, and was used in combination with a thin steel sheet that had not been subjected to surface treatment and had not been oxidized. The bulk density was 0.6 t/m 3 .

(iv) Steel processing powder (粉): Cutting chips and cutting powder generated when manufacturing screws, machine parts, etc., which are classified into A and B according to the shape and degree of oxidation, but in this embodiment, A combination of "A: ordinary steel cutting chips with little oxidation, chip-shaped ones" and "B: ordinary steel cutting chips somewhat oxidized, perm-shaped ones" were used in combination. The bulk density was set to 0.4 t/m 3 .

(ⅴ) Koseon: It is in the shape of a block by crushing the used casting product. It is classified into A and B depending on the base material, but in this embodiment, "A: 1200 mm or less per side" is used. did. The bulk density was 3.0 t/m 3 .

In addition, "steel processing powder" may have an oil component such as cutting oil adhered to it, and when the oil is burned, it becomes a heat source and affects the power source unit. ) was kept constant. In addition, "high wire" has a low melting point because of high carbon compared to other iron-based scraps, and has good solubility, which affects the power source unit.

After blending a plurality of the above scrap species and adjusting the bulk density, the iron-based scrap was charged into the preheating chamber 2 by the supply bucket 13 . In addition, iron-based scrap was charged into the preheating chamber 2 for a sufficient time for the inside of the preheating chamber 2 to be replaced with a predetermined composition according to the capacity of the preheating chamber 2 , while maintaining the composition constant.

The apparent bulk density P of the iron-based scrap charged into the preheating chamber 2 (that is, the iron-based scrap filled in the preheating chamber 2) is, +(shredder bulk density)×(shredder blending ratio)+(new end bulk density)×(new end blending ratio)+(steel processed powder bulk density)×(steel processed powder blending ratio)+(high wire bulk density)×(high wire blending ratio) was calculated. Therefore, for example, in the case of No. 1, apparent bulk density (P) = 0.5 t/m 3 (heavy bulk density) x 0.70 (heavy blending ratio) + 1.3 t/m (shredder bulk density) x 0.10 (shredder blending) It is calculated as ratio) +0.4t/m3 (strength processing powder bulk density) x 0.18 (steel processing powder mixing ratio) + 3.0t/m3 (high wire bulk density) x 0.02 (high wire mixing ratio) = 0.61 t/m3.

During operation, the temperature and oxygen concentration of the exhaust gas were measured at the position of the exhaust port 21 of the preheating chamber 2 , and this oxygen concentration was defined as the oxygen concentration in the preheating chamber 2 . In Table 1, the results and the power source unit index are presented under different operating conditions (used iron-based scrap, apparent bulk density (P) of iron-based scrap in the preheating chamber, and iron-based scrap filling ratio H _SC /H _SF , carbon · Oxygen ratio (C/O) is shown together. In addition, the iron-based scrap filling ratio H _SC /H _SF of Table 1 has shown that it fluctuate|varied in the numerical range during operation. Here, the power source unit index is an evaluation index of the dissolution experiment, and the power source unit of No. 10 [kWh/ton of hot water] is 100, and the ratio of the power source unit of each example to it is shown. Evaluation was made into "○" (pass) when the power source unit index was less than 100, and "x" (failed) when the power source unit index was 100 or more.

According to Table 1, it can be seen that all of the invention examples have a power source unit index of less than 100, and can economically dissolve scrap with high energy use efficiency.

1 melting chamber
1a space part
2 Warm-up room
3 extruder
4 furnace cover
5 electrode
6 exhaust duct
7 Oxygen Blowing Lance
8 Charcoal Blowing Lance
9 Auxiliary smoke burner
10 furnace wall
11 Exit
12 Exit
13 Feed Bucket
14 hot water door
15 publication door
16 running bogie
20 Scrap loading entrance
21 exhaust port
x iron scrap
m molten iron
s molten slag
A arc heating element

Claims (6)

A melting chamber (1) for melting iron-based scrap by arc heating, and a shaft-type preheating chamber (2) extended above the melting chamber (1) for preheating iron-based scrap are provided. In one electric furnace, iron-based scrap is sequentially charged into the preheating chamber 2, so that the iron-based scrap is filled in the preheating chamber 2, and the exhaust generated in the melting chamber 1 The iron scrap is preheated by passing the gas through the preheating chamber 2 filled with the iron scrap, and the preheated iron scrap is sequentially descended in the preheating chamber 2 and supplied into the melting chamber 1, A method of obtaining molten iron by melting iron-based scrap in a melting chamber (1), the method comprising:
The apparent bulk density P of the iron-based scrap filled in the preheating chamber 2 is 0.50t/m3 or more and less than 1.00t/m3, and the iron-based scrap filling ratio H in the preheating chamber 2 _SC /H _SF (however, H _SC : filling height of iron scrap in preheating chamber [m], H _SF : height in preheating chamber [m]) is 0.5 to 0.8, iron scrap in preheating chamber 2 is charged,
Carbon material is used as an auxiliary heat source for dissolving iron-based scrap in the melting chamber 1, and in the melting chamber 1, the carbon/oxygen ratio C/O (however, C: the amount of carbon in the carbon material [kg], O: A method for producing molten iron by an electric furnace, characterized in that oxygen and carbon ash are blown so that the oxygen blowing amount [Nm 3 ]) is 0.70 or more. The method according to claim 1,
A method for producing molten iron by an electric furnace, characterized in that the oxygen concentration in the preheating chamber (2) is less than 15 vol%. The method according to claim 1 or 2,
In an electric furnace characterized in that the injection amount of carbon ash into the melting chamber 1 is 0.3 to 1.4 (kg/min)/ton of tapping, and the amount of blowing of oxygen is 20 to 40 (Nm3/hr)/ton of tapping A method of manufacturing molten iron by 4. The method according to any one of claims 1 to 3,
A method for manufacturing molten iron by an electric furnace, wherein one or more supporting smoke burners are installed in the melting chamber (1), and the iron-based scrap and molten iron in the melting chamber are heated by the supporting smoke burners. 5. The method according to any one of claims 1 to 4,
In the electric furnace, the preheating chamber 2 is extended in the upper part of the position away from the arc heating part of the melting chamber 1, and the scrap charging port 20 is installed in the upper part of the preheating chamber 2,
The iron-based scrap charged into the preheating chamber 2 from the scrap charging port 20 is filled in the space portion 1a of the preheating chamber 2 and the melting chamber 1 below it, and the space portion 1a A method for producing molten iron by an electric furnace, characterized in that the iron-based scrap of the is sequentially extruded toward the arc heating unit. 6. The method of claim 5,
A method for producing molten iron by an electric furnace, characterized in that the iron-based scrap of the space portion (1a) is sequentially extruded toward the arc heating unit by an extruder (3).

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